THE Romans of the easy class dreamed of junketing in a villa with an outlook on cultivated fields. A hundred years ago the Alps were never spoken of without laying stress upon their terrors. Such facts show how different are the tastes and the ideals of this generation from those of our ancestors. In the present age of tiresome security, we have become amateurs of danger. One man scales the highest mountain-peaks without any other purpose than to taste for a few hours the rough pleasure of the struggle for existence. Another prefers risks that will contribute to the increase of man's scientific capital, and will leave something more than a simple personal recollection. I invite the exuberant forces of living youth to the exploration of the sea, than which a vaster field and one more capable of satisfying daring and curiosity of every kind can not be found. It is an exploration which, with all deference to cabinet naturalists, presents at once a great attraction and a high scientific importance.

I know persons whose ideal consists in getting preserved specimens, no matter how many, provided they are new. We call new a species that has not yet been dressed up with a Latin name, and which we have consequently a right to baptize with a word in a dead language, followed by the name of the baptizer. The harm of the matter is in the latter element, for, without that addition, the number of Latin names would be reduced by a half, and there would be no occasion to protest against authors who create a genus for each new species. Some find their pleasure in classifying and naming species. Others profess to despise that occupation. They prefer to dissect animals and describe their anatomy, without concerning themselves respecting the use to which the organs are fitted. Still others love to describe the development of beings, without knowing anything of the purpose of the successive organizations of larvæ and young; and they meet in the work anomalies that puzzle their brains. We understand the swallow, because we see its actions. But if there were naturalists living on the bottom of the ocean who had never been in the air, and who knew these graceful birds only through specimens preserved in alcohol, what brilliant zoölogical, anatomical, and embryogenical dissertations would they not make on the subject! I know many among naturalists occupying themselves with marine zoölogy who do not dive or swim, and whose science is of no more value than the swallow-science of our supposed submarine naturalists would be. We recognize their excuse. It is, that means of observing marine animals in life, aquariums, and especially the diving-dress, are not within everybody's reach. They cost considerable sums. The student needs a diving-jacket, a boat of considerable tonnage, and a crew of competent men, all to himself and under his orders; for freedom is a great element of success in all scientific investigation.

The diving-jacket is a more ingenious and more useful invention than many that make more noise. It is dangerous or safe according to the way it is used. It has come into extensive use. Every seaport, every war-vessel, and every large steamer has a diving dress and apparatus. Even sponge-fishers have recourse to it. Science, however, could derive no profit from the reports of professional divers; their veracity is below everything that could be imagined, and then they look without seeing. Although inhabited by millions of negroes, Africa remained unknown till educated white men succeeded in crossing it; the bottom of the sea will never be known till good observers have gone down there.

Students should descend themselves; but, unfortunately for science, persons are rare who have gone to see in place the animals concerning which they have written large books. They might have been spared many errors. Some have not the means; others are afraid; and still others have once gone down two or three metres, and then hurried to fill the press with the creations of their imagination; for the first plunge which one makes is of no value for the observation of things that are outside of himself. He sees thirty-six colors, and that is all.

This first plunge leaves no agreeable memories. They dress you as if you had to endure the cold of Siberia, a precaution which I have found useless in the Mediterranean. With knit woolen hose, cap, and shirt, I have never felt the cold. Then comes the ample coat, which we get into through the neck-hole, and the casque, which resounds as if one had his head in a kettle. Then they put on you a belt with a dagger, shoes with leaded soles, and lead at your breast and back. Now you are so loaded that you could hardly stand straight if the boat should tip—then you go down into the water where all the weight is no longer felt.

Now a different feeling begins. At the command, "Pump!" some one rapidly screws down the glass in front of your casque, and you hear a noise to which you have to accustom yourself—pah! pah! pah!—accompanied by a hissing of the air. Little whiffs of air come to you, scented with machine oil and caoutchouc. The beginner fails to manage the escape, and his coat and sleeves become inflated, so that, when he wants to go down, he floats like those frogs we used to blow up when we were boys, and then throw upon the water to amuse ourselves with their vain struggles to get under it.

Then comes the gurgling of the water and air escaping through the valve, and you descend. The pressure immediately increases at the rate of one atmosphere for about every ten metres of depth. This increased pressure, which would he insupportable if it was unequally distributed, is hardly felt, because it is exerted in every direction. The air is reduced to half its former volume, so that our inspirations take in double the usual quantity. Instead of breathing more easily, as one would naturally suppose he would do, the diver feels an oppression which is very troublesome at first. But it soon passes away. It is caused by a pressure on the alveoli of the lungs which impedes the exchange of gases. But the equilibrium is soon restored spontaneously.

The most disagreeable sensation produced by the descent consists of pains in the ears, sharp and accompanied by a feeling of dizziness. It is caused by a pressure of the air contained in the medial ear; the tympanum is stretched and pushed upon the ossicles, till a bubble succeeds in making a passage for itself through the Eustachian tube. The pain then ceases, but returns as the descent is continued. After a few plunges, the Eustachian tube enlarges enough to let the air pass freely, and the pains cease. The dizziness is explained by the fact that the inner ear, as M. Delage and other physiologists have shown, is the seat of the sense of direction; so the novice does not know where he is, and imagines that his head is down. Mariners, in training for diving, are caused to go down first in a spot where there is hardly water enough to cover the casque; they come back with downcast features and the flurried air of a man afflicted with vertigo.

The most delicate point is the regulation of the air-escape. The novice lets out too much air, and water comes in by the valve, and the casque seems so heavy that he imagines he is nailed to the bottom. He then lets too much air accumulate, his coat swells, and the casque rises so much as to take the valve out of reach of the hand. Despite all his efforts to stay on the bottom, he springs up to the surface. The air, released from the pressure, expands, the coat is inflated almost to bursting, and he floats like a dead body. One can never be a good diver till he learns to regulate the air as a horseman holds the reins—without thinking about it. We might, indeed, adjust the valve for a particular depth, so that it shall act automatically; but the diver who desires to ascend and descend at will, will do better to keep the escape-valve taut, and regulate it with his head.

The beginner is not able to travel about as he wants to—first, because he feels too light or too heavy, according to the quantity of air in his coat; and, second, because the water offers an unexpected resistance to his progress. He sees things two steps away that he wants to get, and can not reach them.

Pictures show the diver walking along on the bottom of the sea as he would do on the land; it is a false representation. One can not get along without bending his whole body at an angle of forty-five degrees in the direction he wishes to go, and then pushing along on tip-toe in an attitude that would excite laughter in a beholder, assisting himself with his arms as in swimming. If the bottom is uneven, he will do better to creep on his hands and knees.

On the other hand, one can do things in the water that are impossible in the air—let himself drop, for example, from the rocks; the water will break the fall. Or, he can climb cliffs by letting a little air collect in his coat and planting the ends of his fingers in the cracks and rough places. On broken ground he can pass with a kind of flying leap from one rock to another. But all this supposes a degree of familiarity which is not acquired for a considerable time. In my first efforts I cut my hands terribly, and was not able to use my pen or pencil for several days. I tried a coat made with the sleeves ending in India-rubber gloves, but they prevented my picking up small things, and, moreover, did not last long. I then returned to the common sleeves, closed at the wrist, and used knit woolen gloves.

Another difficulty is occasioned by the glasses of the casque becoming covered with the vapor that results from the condensation of the moisture of the breath. The colder the water, the thicker the vapor is. No means as yet tried to get rid of it have resulted satisfactorily, but I have solved the problem by rubbing the glasses with glycerin. The mist then condenses in a uniform nap which does not obscure the glass.

When all these difficulties have been surmounted, there is still one that persists—that is, the effect and the danger of compression and decompression. That imposes a limit to the depth a man can reach with the diving-dress. Divers are liable to two kinds of accidents. One is a prostration on coming to the surface, for which restorative measures often have to be applied; and which, according to Paul Bert, results from the effects of the change of medium on the spinal marrow. It is rarely mortal, but may eventually produce a paralysis of the lower limbs. The other accident, graver but very rare, consists of a gaseous embolism of the capillaries of the lung, produced by the disengagement of bubbles of air in the blood, which has dissolved too much of it while under high pressure. The action is like that of Seltzer water at the moment of pressing on the pedal of the siphon. Under its effects, when it occurs, the diver dies as soon as he reaches the surface.

Both causes of accident can be avoided by descending and rising slowly. For this reason a steel chain may be used as a ladder, to be let down to the depth the diver has reached, by the aid of which he can stop at will while coming up. But the question of time comes in to limit the depth which it is possible to reach. If we allow three quarters of an hour for a diving excursion, a quarter of an hour will be required to descend below thirty metres, and as long to come up; so that only a quarter of an hour is left for staying on the bottom.

Of the scientific observations which I have been able to make with the diving-dress, I will speak only of those of a physical order; a book would not be sufficient to describe my zoölogical observations. When the water is transparent and the sun shining, we can, looking down from the boat, distinguish the bottom to about twenty metres; but for that the surface should be perfectly smooth. I have had fixed in the bottom of my yacht Amphiastre a light-port with a very thick glass. By darkening the cabin we can see through it clearly, farther than twenty metres, even when the surface of the sea is troubled. Seen thus from above, the bottom of the sea always looks flat. All the visible parts are equally lighted, and the appearance of relief is naturally destroyed by the absence of projected shadows. In going down in the diving apparatus, we are astonished at perceiving that the ground, which appeared nearly uniform, is really bristling with rocks and hollowed by deep valleys. The shadows are now visible, because the light coming from above, the parts under the projections of the rocks and the tufts of sea-weed are in the dark. If the diver looks up from the bottom through the frontal glass of his casque, he will see a great light, circular space that may be regarded as the base of an inverted luminous cone, of which the spectator's eye occupies the tip, and the apical angle of which is about 62° 50'. Beyond this circle the surface looks dark, presenting precisely the aspect of the sea as seen when looking down into it from the boat. The sky and objects in the air are visible only within the limits of the luminous circle. The borders of this circle are always more or less indented, for the surface is never perfectly quiet. The sunbeams are dimmed and come down in dancing showers as we see them in a room on the edge of the water when the blinds are drawn down, and the rays, reflected from the mobile surface, shine upon the ceiling of the room.

The decrease of density of the sun's rays is very rapid, and they are almost completely diffused at thirty metres. As the sun declines toward the horizon, a darkness suddenly comes on which has sometimes caused me to ascend very speedily, in the belief that night had fallen. Coming out of the water, I was astonished to find myself immersed in the rays of a sun not yet near setting. There is an angle at which the proportion of rays reflected to rays refracted becomes so much against the latter that the illumination of the bottom falls off very abruptly.

The transparency of the water along the littoral varies enormously. In times of rain, it is clouded by swollen streams pouring into it; in dry and still weather it becomes nearly as clear as in the open sea. There are also capricious and sudden changes caused by currents from the land or from the open sea, which are capable of producing great effects in a few hours. Experiments on the penetration of light, to have any value, should be made very far out.

When the water is comparatively clear, it still absorbs so much light that at thirty metres' depth, if the sky is clouded, one can not see distinctly enough to collect small animals. In a horizontal direction one can not distinguish a rock more than seven or eight metres off. When the sun is shining and the water is very clear, we can see a bright object at twenty or even perhaps at twenty-five metres. But in usual conditions we have to content ourselves with half these numbers. These facts, verified many times in the descents which I have executed with the diving apparatus of my laboratory at Nice during the last three years, appear to me important from several points of view.

It is evident that a submarine boat can not see its way under these conditions. Slow as may be its movement, there will not be time for it to retreat if it sees some obstacle rising in front of it; for it would not be more than ten metres away from the impediment at the moment of perceiving it. It will always have to take its directions before going down, and to sail only upon a ground the relief of which has been carefully explored. Submarine navigation will thus always be confined to limits which the genius of man—since it can not change the transparency of water—will never be able to enlarge.

These observations are also of great interest from a biological point of view. We can see every day that agile marine animals living in the illuminated strata of the waters—fishes, lobsters, and cephalopods—are in the habit, when they are frightened, of giving themselves up to a very rapid flight and quickly stopping. They feel that a few metres are enough to put them out of the range of vision of their pursuer. Some even take the pains to add to the obscurity of the water by discharging their ink, as the squids do, or stirring up the mud, after the manner of many fishes. Marine animals may well be near-sighted; for of what use to them is a long vision when they can at most see only a few metres away? Hence their crystalline lens is bulged into a nearly spherical shape. They live in a world of surprises, and, as it were, in a perpetual fog. The nets we stretch for them would hardly take any fish, at least in the daytime, if they could see as far as we see in the air.

The color of water varies from blue to greenish, usually according to the degree of its clearness. Objects at twenty metres' depth begin to take a bluish hue, and at from twenty-five to thirty metres the light is so blue that dark-red animals look black, while green and bluish sea-weeds seem almost white by contrast. Coming back quickly into the air, eyes accustomed to the blue light see the air-landscape red. The red rays are extinguished first, a fact which had been already demonstrated by laboratory experiments. The blue rays, being absorbed in a less degree, penetrate farther; and these are the rays which act most energetically on the photographic plate. This fact disposes of the objections which some students have repeated with a persistency that is not creditable to their ideas of physics, against the use of photographic plates in determining the depth to which daylight can penetrate through water.

When there is a swell, the diver's task is a hard one. He is constantly tossed about in spite of himself, and an irresistible force compels him to swing like a pendulum. This oscillation of the water, which is a counterpart of the waves of the surface, is nearly as perceptible at thirty metres as at ten metres. It can not be a surf phenomenon, for fishermen find that, after a storm, depths of fifty metres and more are swept by it. Special apparatus and experiments are required to determine to what depth it extends; but, in view of the incompressibility of water, I should not be astonished to find it extending very far down. In this matter, as well as in a great many others, the diver is in a condition to gain valuable information by which new avenues may be opened for the study of the phenomena of Nature.—Translated for The Popular Science Monthly from the Revue Scientifique.